It has been conventionally known that cycloalkanol and/or cycloalkanone can be oxidized with nitric acid to an alkanedicarboxylic acid at elevated temperatures. There is also a known method for manufacturing an alkanedicarboxylic acid by oxidizing cycloalkanol and/or cycloalkanone with nitric acid using an adiabatic reactor. JP-B-43-19529, for example, discloses a continuous one-step manufacturing method for an alkanedicarboxylic acid by oxidizing cycloalkanol, cycloalkanone or cycloalkylamine and/or ω-hydroxylalkane dioic acids having at least 4 carbon atoms and lactones thereof or tetrahydrofuran with nitric acid at elevated temperatures in a recirculating system, wherein starting materials are vigorously mixed with 80 to 400 times the amount in volume of 40 to 70% nitric acid. The amount of nitric acid is adjusted so that the reaction temperature during the reaction does not exceed 25° C. The reaction proceeds at 45 to 90° C. under a normal pressure or a pressurized condition, and the reaction mixture coming out from a reaction zone is separated from nitrogen oxide after 4 minutes or less of residence time. The concentration of nitric acid is raised again up to the concentration nearly equivalent to the concentration in the reaction zone by evaporating water from the reaction mixture, and an alkanedicarboxylic acid is separated from a part of the reaction mixture by an usual method. The mother liquid is added to the remaining part of the reaction mixture, and the thus joined mixture is vigorously mixed with fresh starting materials and returned to the reaction zone. The disclosure describes that the mixing of nitric acid and starting materials (i.e. cycloalkanol, cycloalkanone or cycloalkylamine and/or ω-hydroxylalkane dioic acids having at least 4 carbon atoms, lactones thereof or tetrahydrofuran) is preferably performed within as short a time as possible when nitric acid (i.e. nitric acid sent to a circulation line and/or nitric acid freshly fed) is introduced into the reaction zone after having been mixed with the starting materials. The disclosure describes that it is preferable to mix them so that the starting materials are dissolved into a transparent state within 5 seconds at the latest using, for example, an injector, a mixing nozzle or a turbine mixer. Particularly, in the case of oxidation of cyclohexanol and cyclohexanone, it is disclosed to make an effort to obtain a transparent solution within 0.05 to 0.1 seconds after mixing. It describes that the reason for this is that a longer mixing time causes a local elevation of temperature in the reaction zone, resulting in a decrease in yield of an alkanedicarboxylic acid. However, even with the mixing time described in JP-B-43-19529, a yield of an alkanedicarboxylic acid is not necessarily high. This means that the mixing time defined in JP-B-43-19529 is not adequate.
It is also known in other literature that a higher temperature lowers a yield of adipic acid in oxidizing cyclohexanol and/or cyclohexanone with nitric acid to obtain adipic acid. For example, “Preparation of adipic acid by oxidizing cyclohexanol and cyclohexanone with nitric acid”, W. J. VAN ASSELT and D. W. VAN KREVELEN, Rec. Tra. Chem., 82, 51–67, 429–437, 438–449 (1963) shows that yield of adipic acid lowers at a high temperature, in particular, not lower than 60° C., even in the presence of a copper catalyst, from results of a batch oxidation reaction test using a cylindrical vessel equipped with a magnetic stirrer and a cooling jacket.
Therefore, in JP-B-43-19529, a reaction is recommended to proceed at the temperature of 45 to 90° C. under a normal pressure or a pressurized condition, though a residence time or a mixing time is regulated within an extremely short time. Further, examples in JP-B-43-19529 clearly describes an outlet temperature to be 70° C.
On the other hand, it is also clear that a concentration of nitric acid required for obtaining the same yield of adipic acid increases with lowering of temperature based on a calculation using the reaction rate of cyclohexanol or cyclohexanone to adipic acid obtained in the same literature; “Preparation of adipic acid by oxidation of cyclohexanol and cyclohexanone with nitric acid”, W. J. VAN ASSELT and D. W. VAN KREVELEN, Rec. Tra. Chem., 82, 51–67, 429–437, 438–449 (1963).
This means that, in conventional technology, lowering the temperature requires a higher amount of nitric acid in the oxidation reaction to give an increased yield of adipic acid. That is, the method shown in the above described JP-B-43-19529 has a problem in that a high amount of nitric acid is consumed due to oxidizing cyclohexanol and/or cyclohexanone with nitric acid at low temperatures such as 45 to 90° C.
JP-B-48-21088 describes a method for reducing the amount of nitric acid consumed. Said official gazette discloses a method for converting cycloalkanol and/or cycloalkanone to an alkanedicarboxylic acid by a liquid-phase oxidation with nitric acid, wherein only small amounts of nitric acid are essentially consumed. More specifically, it discloses a method for manufacturing an alkanedicarboxylic acid by a liquid-phase oxidation of reaction components selected from the group consisting of cycloalkanol and cycloalkanone with nitric acid, which has improved the reduction in the amount of nitric acid consumed, wherein said reaction components are contacted with nitric acid in the presence of a copper-vanadium catalyst at 90 to 140° C., at least a part of the reaction mixture comprising 0.30 to 0.60% by weight of oxidized copper, 0.01 to 0.50% by weight of oxidized vanadium and a reduction product of nitric acid having an average oxygen/nitrogen ratio larger than 0.5 is circulated, wherein a weight ratio of circulation flow to reaction components is maintained at 200 to 1300 and a product of said weight ratio and the concentration of the oxidized vanadium is maintained at 30 to 60, followed by recovering said alkanedicarboxylic acid. Circulation here means a circulation only in a reaction system, which is different from “total circulation flow” of an aqueous nitric acid solution of the present invention described below. In this description, this circulation is defined as “circulation flow in reaction system”.
Furthermore, JP-B-48-21088 describes that a suitable mixing apparatus such as draft-tube-mixer may be used to reduce the difficulty of mixing of the flow by mixing the incoming flow of the cycloalkanol and/or cycloalkanone with the circulation flow in the reaction system from the reaction apparatus. This method, however, requires that the weight ratio of the circulation flow in the reaction system of the reaction components is set at an extremely high level such as 200 to 1300. A large volume of circulation flow in the reaction system requires a large pump capacity to ensure such a large circulation volume as well as pipe lines and a reactor considering the pressure loss, and is thus disadvantageous with respect to equipment cost and proportional cost of power.
As listed above, although various methods for oxidizing cycloalkanol and/or cycloalkanone to an alkanedicarboxylic acid with nitric acid are known, they require maintaining a reaction zone at a temperature not higher than 90° C. or require an extremely large amount of circulation flow of nitric acid in the reaction system in the case of temperatures above 90° C., to improve the yield of alkane dioic acid. In addition, temperatures in the reaction zone not higher than 90° C. has problems such as a large amount of nitric acid consumption, a large volume of air in a stripper tower and a large volume of total circulation flow of an aqueous solution of nitric acid containing the alkanedicarboxylic acid product which is wholly circulating within the system, thus resulting in increased loads of a crystallizer and a concentration tower. Temperatures above 90° C. also has a problem of an extremely large amount of nitric acid circulation flow in a reaction system to maintain a yield of the alkanedicarboxylic acid.